Wireless energy transfer system

ABSTRACT

A wireless energy transfer system includes a first energy transfer unit having at least one resonant frequency, a second energy transfer unit having the at least one resonant frequency, and a load. The first wireless energy transfer unit includes a first coil magnetically coupled to a first wireless energy transfer cell, and the second wireless energy transfer unit includes a second coil magnetically coupled to a second wireless energy transfer cell. The first coil receives first energy and through the magnetic coupling between the first coil and the first wireless energy transfer cell, the first wireless energy transfer cell is caused to generate second energy, wherein the second wireless energy transfer cell receives the second energy and through the magnetic coupling between the second wireless energy transfer cell and the second coil, the second coil is caused to provide third electromagnetic wave energy to the load.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) from U.S.Provisional Application No. 61/096,466, entitled “Apparatus for WirelessPower and Data Transfer Over a Distance,” which was filed on Sep. 12,2008, and U.S. Provisional Application No. 61/165,134, entitled“Wireless Energy Transfer System,” which was filed on Mar. 31, 2009, thedisclosures of which are incorporated herein by reference.

GOVERNMENT CONTRACT

This work was supported in part by Army grant No. W81XWH05-C-0047. TheUnited States government may have certain rights in the inventiondescribed herein.

FIELD OF THE INVENTION

The present invention relates to the transfer of energy wirelessly, andin particular to a wireless energy transfer system, and wireless energytransfer units and cells employed thereby, that allows energy, such asRF energy, to be transferred wirelessly using nonradiative resonantcoupling for power transfer and/or data communications purposes.

BACKGROUND OF THE INVENTION

In recent years, rapid technological advances in microelectronics,nanotechnology and MEMS technology have spurred new types of microdevices and sensors, such as RFID, micro cameras, accelerometers,miniature implantable devices, and micro chemical sensors, playingimportant roles in industrial automation, military applications,homeland security, environmental monitoring, and biomedicine. Thesetechnological advances have also resulted in significant impacts onpeople's daily lives. For example, mobile electronic devices, such asthe laptop computer, cell phone, and personal media player, have becomean inseparable part of many people. All these electronic devices rely onelectrical energy to power their circuits, and most of them require acommunication channel to exchange information with certain host devices,computers or systems. Currently, batteries and wireless technologies areutilized for these purposes. However, in many cases, these solutions areinadequate. For example, running out of battery power in a laptop or acell phone when a recharging procedure is missed is an unpleasant, butcommon event. It would be highly desirable if, when a laptop, cellphone, media player or other electronic device is located within a “hotspot”, a wireless router will not only transmit/receive information, butalso recharge these devices. With such a technology, these personaldevices will not need manual recharging, and their batteries can be madesmaller since they are recharged more frequently. Such a wireless energytransfer technology could also be used in other consumer and industrialapplications, such as transferring power from a solar panel outside aresidential house to the inside without a cable through the constructionwall or roof, powering devices or systems inside a sealed, pressured, orvacuum container of either air or liquid, powering and guiding a robotor a vehicle by a series of thin energy cells under the floor or pavedroad, recharging an electric car by a low-profile wireless charger “mat”on the garage floor, or transferring solar energy to the inside of aparked car to power ventilation fans in order to keep the insidetemperature from rising too high, to name just a few.

In the medical field, microelectronic devices can be implanted withinthe human body to perform a variety of therapeutic, prosthetic, anddiagnostic functions. The deep brain stimulation (DBS) device, forexample, is used as a brain implant for treating Parkinson's disease andessential tremor. Currently, a surgical procedure is required to replacethe entire device when its battery power is depleted. The combined costfor this procedure is approximately $25,000, which has been described as“the world's most expensive battery change.” Wireless energy transfertechnology can eliminate the need for these costly replacements.

One particular medical problem of high interest is the design of awireless network of devices for the human body. Current and futurewireless sensors will be able to be patched on the skin or the undersideof clothes to perform a variety of important tasks, such as monitoringvital signs and levels of physical activity. Microsensors may also beimplanted by either surgery or injection into the inside of the body toperform additional tasks, such as restoring lost vision, hearing, andmotor functions, releasing drugs, and monitoring cancer orcardiovascular diseases. In the military, a body sensor network embeddedwithin the clothes is highly desirable since it can potentially producewarning signals of imminent attacks, detect the presence of people orobjects of interest, monitor chemicals in the air, evaluate wounds, andcommunicate with a central station or an assistive device such as arescue robot.

While the high significance of such a body network has been recognizedby both the research community and industry, the problem of providingpower and communication functions to a highly distributed network ofelectronic devices without wired connections and batteries has not beensolved.

SUMMARY OF THE INVENTION

In one embodiment, the invention provides a wireless energy transfersystem that includes a first wireless energy transfer unit having atleast one resonant frequency, a second wireless energy transfer unithaving the at least one resonant frequency, and a load. The firstwireless energy transfer unit includes a first coil magnetically coupledto a first wireless energy transfer cell, wherein the first wirelessenergy transfer cell comprises a first LC resonant tank including afirst conductor coil coupled to at least one first insulator, andwherein the at least one first insulator forms a part of at least onecapacitor of the first LC resonant tank. The second wireless energytransfer unit includes a second coil magnetically coupled to a secondwireless energy transfer cell, wherein the second wireless energytransfer cell comprises a second LC resonant tank including a secondconductor coil coupled to at least one second insulator, and wherein theat least one second insulator forms a part of at least one capacitor ofthe second LC resonant tank. The first coil receives firstelectromagnetic wave energy, wherein in response to receipt of the firstelectromagnetic wave energy and through the magnetic coupling betweenthe first coil and the first wireless energy transfer cell the firstwireless energy transfer cell is caused to generate secondelectromagnetic wave energy, wherein the second wireless energy transfercell receives the second electromagnetic wave energy, wherein inresponse to receipt of the second electromagnetic wave energy andthrough the magnetic coupling between the second wireless energytransfer cell and the second coil the second coil is caused to providethird electromagnetic wave energy to the load. In one particularembodiment, the second electromagnetic wave energy is generated in afirst nonradiative near field of the first wireless energy transfercell, and the second electromagnetic wave energy is received in a secondnonradiative near field of the second wireless energy transfer cell,wherein the first nonradiative near field overlaps the secondnonradiative near field. The first wireless energy transfer unit mayhave a plurality of resonant frequencies and the second wireless energytransfer unit may also have the plurality of resonant frequencies.

In one particular embodiment, the first wireless energy transfer unithas at least a first resonant frequency and a second resonant frequency,and the second wireless energy transfer unit also has the first resonantfrequency and the second resonant frequency, wherein the first, secondand third electromagnetic energies are each at the first resonantfrequency and the third electromagnetic energy is used to provide powerto at least a portion of the load. In addition, the first coil receivesfourth electromagnetic wave energy at the second resonant frequency,wherein in response to receipt of the fourth electromagnetic wave energyand through the magnetic coupling between the first coil and the firstwireless energy transfer cell the first wireless energy transfer cell iscaused to generate fifth electromagnetic wave energy at the secondresonant frequency, wherein the second wireless energy transfer cellreceives the fifth electromagnetic wave energy, wherein in response toreceipt of the fifth electromagnetic wave energy and through themagnetic coupling between the second wireless energy transfer cell andthe second coil the second coil is caused to provide sixthelectromagnetic wave energy at the second resonant frequency to theload, and wherein the fourth, fifth and sixth electromagnetic waveenergies are used to communicate information to the load. Also, thefourth electromagnetic wave energy may be modulated based on theinformation.

In another embodiment, the invention provides a wireless energy transferunit having at least one resonant frequency that includes an energycoupling/extraction coil, and a wireless energy transfer cellmagnetically coupled to the energy coupling/extraction coil. Thewireless energy transfer cell comprises an LC resonant tank including aconductor coil coupled to at least one insulator, wherein the at leastone insulator forms a part of at least one capacitor of the LC resonanttank. The energy coupling/extraction coil may comprise a single loopcoil or a plurality of loops.

In one particular embodiment, the at least one insulator includes afirst surface and a second surface opposite the first surface, whereinthe conductor coil is coupled to the first surface, wherein the LCresonant tank further includes a plurality of conductive strips coupledto the second surface, and wherein the conductor coil, the at least oneinsulator and the plurality of conductive strips form the at least onecapacitor of the LC resonant tank. The at least one insulator may be acylindrical insulator, wherein the conductor coil is a helical conductorcoil. In one particular embodiment, each of the conductive strips coversonly two adjacent portions of the helical conductor coil. The at leastone insulator may also be a flat insulator, wherein the conductor coilis a flat conductor coil and wherein each of the plurality of conductivestrips is a flat conductive strip. The conductor coil may be a squarespiral or a circular spiral. In another alternative, the conductor coilincludes a plurality of crisscrossing portions along a length thereofsuch that a beginning and an end of the conductor coil are positionedadjacent to one another.

In still another particular embodiment, the at least one insulatorincludes a first surface and a second surface opposite the firstsurface, wherein the conductor coil is coupled to the first surface,wherein the LC resonant tank further includes a second conductor coilcoupled to the second surface, wherein the conductor coil and the secondconductor coil are electrically coupled to one another, and wherein theconductor coil, the at least one insulator and the second conductor formthe at least one capacitor of the LC resonant tank. The conductor coiland the second conductor coil may be positioned on the insulator suchthat they overlap and correspond to one another as they wind around theinsulator. Also, the at least one insulator may be a cylindricalinsulator, wherein the conductor coil and the second conductor coil areeach a helical conductor coil, or, alternatively, the at least oneinsulator may be a rectangular insulator, wherein the conductor coil andthe second conductor coil are each a rectangular conductor coil.

In another embodiment, the at least one insulator includes an outercylindrical insulator and an inner cylindrical insulator, the outercylindrical insulator and the inner cylindrical insulator beingstructured to rotate relative to one another, wherein the LC resonanttank further includes a first conductor sheet coupled to the outercylindrical insulator and a second conductor sheet coupled to the innercylindrical insulator, wherein the outer cylindrical insulator, theinner cylindrical insulator, the first conductor sheet and the secondconductor sheet form the at least one capacitor, wherein a capacitanceof the at least one capacitor may be varied by rotating the outercylindrical insulator and the inner cylindrical insulator relative toone another, and wherein the conductor coil is a helical conductor coilhaving a first end coupled to the first conductor sheet and a second endcoupled to the second conductor sheet. Preferably, the first conductorsheet extends along about 50% of the outer cylindrical insulator and thesecond conductor sheet extends along about 50% of the inner cylindricalinsulator to provide maximum variability of the at least one capacitor.

In still another embodiment, the at least one insulator is a cylindricalinsulator, wherein the LC resonant tank further includes a firstconductor ring coupled to an inner surface of the cylindrical insulatorand a second conductor ring coupled to an outer surface of thecylindrical insulator, wherein the first conductor ring has a first gapformed therein and the second conductor ring has a second gap formedtherein, wherein the cylindrical insulator, the first conductor ring andthe second conductor ring form the at least one capacitor, wherein theconductor coil is a helical conductor coil having a first end coupled tothe first conductor ring and a second end coupled to the secondconductor ring, and wherein the LC resonant tank further includes aferromagnetic core provided within the conductor coil. The ferromagneticcore may comprise a plurality of ferromagnetic discs.

In another particular embodiment, the at least one insulator is aninsulator film, wherein the LC resonant tank further includes a firstmetal film coupled to a top surface of the insulator film and a secondmetal film coupled to a bottom surface of the insulator film, whereinthe insulator film, the first metal film and the second metal film formthe at least one capacitor, and wherein the conductor coil is a planarconductor coil having a first end coupled to the first metal film and asecond end coupled to the second metal film. The planar conductor coilmay include a plurality of crisscrossing portions along a length thereofsuch that the first end and the second end are positioned adjacent toone another.

In still another embodiment, the invention provides a wireless energytransfer system that includes a transmitter wireless energy transferunit having at least one resonant frequency, a receiver wireless energytransfer unit having the at least one resonant frequency, a number ofrelay units, and a load. The transmitter wireless energy transfer unitincludes a first coil magnetically coupled to a first wireless energytransfer cell, the first wireless energy transfer cell comprising afirst LC resonant tank including a first conductor coil coupled to atleast one first insulator, wherein the at least one first insulatorforms a part of at least one capacitor of the first LC resonant tank.The receiver wireless energy transfer unit includes a second coilmagnetically coupled to a second wireless energy transfer cell, thesecond wireless energy transfer cell comprising a second LC resonanttank including a second conductor coil coupled to at least one secondinsulator, wherein the at least one second insulator forms a part of atleast one capacitor of the first LC resonant tank. Also, each relay unithas a relay wireless energy transfer cell comprising a relay LC resonanttank including a relay conductor coil coupled to at least one relayinsulator, wherein the at least one relay insulator forms a part of atleast one capacitor of the relay LC resonant tank. In this embodiment,the first coil receives first electromagnetic wave energy, wherein inresponse to receipt of the first electromagnetic wave energy and throughthe magnetic coupling between the first coil and the first wirelessenergy transfer cell the first wireless energy transfer cell is causedto generate second electromagnetic wave energy, wherein the number ofrelay units in response to receipt of the second electromagnetic waveenergy cause third electromagnetic wave energy to be generated, whereinthe second wireless energy transfer cell receives the thirdelectromagnetic wave energy, wherein in response to receipt of the thirdelectromagnetic wave energy and through the magnetic coupling betweenthe second wireless energy transfer cell and the second coil the secondcoil is caused to provide fourth electromagnetic wave energy to theload. In one particular embodiment, the transmitter wireless energytransfer unit, the number of relay units and the receiver wirelessenergy transfer unit are arranged in a linear fashion. In anotherparticular embodiment, the transmitter wireless energy transfer unit,the number of relay units and the receiver wireless energy transfer unitare arranged in a non-linear fashion.

The number of relay units may comprise a plurality of relay unitsarranged in the form of a two-dimensional array or a three-dimensionalarray.

The invention also provides a wireless energy transfer method thatincludes steps of (i) receiving first electromagnetic wave energy in afirst conductor, preferably a coil, having a resonant frequency, (ii) inresponse to receiving the first electromagnetic wave energy, causing afirst wireless energy transfer cell to generate second electromagneticwave energy having the resonant frequency through magnetic couplingbetween the first conductor and the first wireless energy transfer cell,the first wireless energy transfer cell comprising a first LC resonanttank including a first conductor coil coupled to at least one firstinsulator, wherein the at least one first insulator forms a part of atleast one capacitor of the first LC resonant tank, (iii) receiving thesecond electromagnetic wave energy in a second wireless energy transfercell, the second wireless energy transfer cell comprising a second LCresonant tank including a second conductor coil coupled to at least onesecond insulator, wherein the at least one second insulator forms a partof at least one capacitor of the second LC resonant tank, and (iv) inresponse to receiving the second electromagnetic wave energy, causing asecond conductor, preferably a coil, to provide third electromagneticwave energy to a load through magnetic coupling between the secondwireless energy transfer cell and the second conductor. Preferably, thesecond electromagnetic wave energy is generated in a first nonradiativenear field of the first wireless energy transfer cell, and the secondelectromagnetic wave energy is received in a second nonradiative nearfield of the second wireless energy transfer cell, wherein the firstnonradiative near field overlaps the second nonradiative near field.

The method may further include steps of (i) receiving fourthelectromagnetic wave energy in the first conductor, the first conductoralso having a second resonant frequency different than the resonantfrequency, (ii) in response to receiving the fourth electromagnetic waveenergy, causing the first wireless energy transfer cell to generatefifth electromagnetic wave energy having the second resonant frequencythrough magnetic coupling between the first conductor and the firstwireless energy transfer cell, (iii) receiving the fifth electromagneticwave energy in the second wireless energy transfer cell, and (iv) inresponse to receiving the fifth electromagnetic wave energy, causing thesecond conductor to provide sixth electromagnetic wave energy to theload through magnetic coupling between the second wireless energytransfer cell and the second conductor. In this embodiment, the thirdelectromagnetic energy is used to provide power to at least a portion ofthe load and the fourth, fifth and sixth electromagnetic wave energiesare used to communicate information to the load.

In another embodiment, a wireless sensor network is provided thatincludes a first wireless energy transfer unit having at least oneresonant frequency, a second wireless energy transfer unit having the atleast one resonant frequency, and a sensor coupled to the secondwireless energy transfer unit. The first wireless energy transfer unitincludes a first coil magnetically coupled to a first wireless energytransfer cell, the first wireless energy transfer cell comprising afirst LC resonant tank including a first conductor coil coupled to atleast one first insulator, wherein the at least one first insulatorforms a part of at least one capacitor of the first LC resonant tank.The second wireless energy transfer unit including a second coilmagnetically coupled to a second wireless energy transfer cell, thesecond wireless energy transfer cell comprising a second LC resonanttank including a second conductor coil coupled to at least one secondinsulator, wherein the at least one second insulator forms a part of atleast one capacitor of the second LC resonant tank. The sensor iscoupled to the second coil of the second wireless energy transfer unit.The first coil receives first electromagnetic wave energy, and inresponse to receipt of the first electromagnetic wave energy and throughthe magnetic coupling between the first coil and the first wirelessenergy transfer cell the first wireless energy transfer cell is causedto generate second electromagnetic wave energy. The second wirelessenergy transfer cell receives the second electromagnetic wave energy,and in response to receipt of the second electromagnetic wave energy andthrough the magnetic coupling between the second wireless energytransfer cell and the second coil the second coil is caused to providethird electromagnetic wave energy to the sensor. The thirdelectromagnetic energy is used to provide power to the sensor.

In one particular embodiment, both power and information is provided tothe sensor. Specifically, the first wireless energy transfer unit andthe second wireless energy transfer unit both have at least a firstresonant frequency and a second resonant frequency different that thefirst resonant frequency. The first, second and third electromagneticenergies are each at the first resonant frequency, and the first coilreceives fourth electromagnetic wave energy at the second resonantfrequency. In response to receipt of the fourth electromagnetic waveenergy and through the magnetic coupling between the first coil and thefirst wireless energy transfer cell the first wireless energy transfercell is caused to generate fifth electromagnetic wave energy at thesecond resonant frequency, wherein the second wireless energy transfercell receives the fifth electromagnetic wave energy, wherein in responseto receipt of the fifth electromagnetic wave energy and through themagnetic coupling between the second wireless energy transfer cell andthe second coil the second coil is caused to provide sixthelectromagnetic wave energy at the second resonant frequency to thesensor. The fourth, fifth and sixth electromagnetic wave energies areused to communicate information to the sensor.

In another particular embodiment, power is provided to the sensor andinformation is received from the sensor. Specifically, the firstwireless energy transfer unit and the second wireless energy transferunit both have at least a first resonant frequency and a second resonantfrequency different than the first resonant frequency. The first, secondand third electromagnetic energies are each at the first resonantfrequency, and the second coil receives fourth electromagnetic waveenergy at the second resonant frequency, wherein in response to receiptof the fourth electromagnetic wave energy and through the magneticcoupling between the second coil and the second wireless energy transfercell the second wireless energy transfer cell is caused to generatefifth electromagnetic wave energy at the second resonant frequency,wherein the first wireless energy transfer cell receives the fifthelectromagnetic wave energy, wherein in response to receipt of the fifthelectromagnetic wave energy and through the magnetic coupling betweenthe first wireless energy transfer cell and the first coil the firstcoil is caused to provide sixth electromagnetic wave energy at thesecond resonant frequency to a data collection unit. The fourth, fifthand sixth electromagnetic wave energies are used to communicateinformation from the sensor to the data collection unit.

The wireless sensor network may also include a third wireless energytransfer unit having the at least one resonant frequency, the thirdwireless energy transfer unit including a third coil magneticallycoupled to a third wireless energy transfer cell, the third wirelessenergy transfer cell comprising a third LC resonant tank including athird conductor coil coupled to at least one third insulator, whereinthe at least one third insulator forms a part of at least one capacitorof the third LC resonant tank. The network in this embodiment alsoincludes a second sensor coupled to the third conductor coil. The thirdwireless energy transfer cell receives the second electromagnetic waveenergy, and in response to receipt of the second electromagnetic waveenergy and through the magnetic coupling between the third wirelessenergy transfer cell and the third coil the third coil is caused toprovide electromagnetic wave energy to the second sensor that is used toprovide power to the second sensor.

The wireless sensor network may be a body sensor network adapted toacquire data relating to physiological or physical parameters of asubject, wherein the sensor is structured to generate the data relatingto physiological or physical parameters of the subject. The firstwireless energy transfer unit in this embodiment is structured to beworn by the subject, and the sensor is structured to be attachedexternally to a body of the subject or implanted in the body of thesubject. Preferably, the second wireless energy transfer cell isstructured to be attached externally to the body of the subject. In onepreferred embodiment, the at least one second insulator includes a firstsurface and a second surface opposite the first surface, wherein thesecond conductor coil is coupled to the first surface, wherein the LCresonant tank further includes a plurality of conductive strips coupledto the second surface, wherein the second conductor coil, the at leastone second insulator and the plurality of conductive strips form the atleast one capacitor of the second LC resonant tank, wherein the at leastone second insulator is a flat insulator, and wherein the secondconductor coil is a flat conductor coil and each of the plurality ofconductive strips is a flat conductive strip.

In still another embodiment, the invention provides a wireless energytransfer unit having at least one resonant frequency that includes anenergy coupling/extraction conductor, such as a coil, and a multi-layerwireless energy transfer cell magnetically coupled to the energycoupling/extraction conductor. The multi-layer wireless energy transfercell includes a top layer and a bottom layer, the top layer and thebottom layer being made of a magneto-electric material that produces anelectric field when exposed to a magnetic field, a first conductor layerforming a first electrode positioned adjacent to the top layer, a secondconductor layer forming a second electrode positioned adjacent to thebottom layer, and a central layer positioned between the first conductorlayer and the second conductor layer, the central layer being made of apiezoelectric material which resonates in response to an electric fieldbeing applied thereto by the first conductor layer and the secondconductor layer.

In still another embodiment, the invention provides, a wireless energytransfer unit is provided that includes an energy coupling/extractionconductor, and a multi-layer wireless energy transfer cell magneticallycoupled to the energy coupling/extraction conductor. The multi-layerwireless energy transfer cell includes a first coil element including afirst insulator layer and a first conductor coil provided on the firstinsulator layer, the first conductor coil including a plurality of firstcrisscrossing portions along a length thereof such that a firstbeginning and a first end of the first conductor coil are positionedadjacent to one another, a second coil element including a secondinsulator layer and a second conductor coil provided on the secondinsulator layer, the second conductor coil including a plurality ofsecond crisscrossing portions along a length thereof such that a secondbeginning and a second end of the second conductor coil are positionedadjacent to one another, and an insulator element made of an insulatingmaterial provided between the first coil element and the second coilelement. The first coil element and the second coil element areelectrically connected to one another, preferably through the insulatorelement. Also, in the preferred embodiment, the multi-layer wirelessenergy transfer cell further includes a third coil element including athird insulator layer and a third conductor coil provided on the thirdinsulator layer, the third conductor coil including a plurality of thirdcrisscrossing portions along a length thereof such that a thirdbeginning and a third end of the third conductor coil are positionedadjacent to one another, and a second insulator element made of aninsulating material provided between the second coil element and thethird coil element, wherein the second coil element and the third coilelement are electrically connected to one another, preferably throughthe second insulator element. The first coil element, the second coilelement, the third coil element, the insulator element, and the secondinsulator element may all be disk-shaped. Also, the first conductorcoil, the second conductor coil and the third conductor coil may each befilm coils.

In another particular embodiment, the invention provides a wirelessenergy transfer unit that includes an energy coupling/extractionconductor, and a multi-layer cylindrical wireless energy transfer cellmagnetically coupled to the energy coupling/extraction conductor. Themulti-layer cylindrical wireless energy transfer cell includes an innercylindrical insulator, a first spiral conductor coil provided on asurface of the inner cylindrical insulator, an insulator layer providedon top of the first spiral conductor coil, and a second spiral conductorcoil provided on a surface of the insulator layer, wherein the secondspiral conductor coil is electrically connected to the first spiralconductor coil. Preferably, the first spiral conductor coil is orientedin one of a positive angle and a negative angle with respect to alongitudinal axis of the inner cylindrical insulator, and the secondspiral conductor coil is oriented in the other of the positive angle andthe negative angle with respect to the longitudinal axis of the innercylindrical insulator. Also, in the preferred embodiment, the firstspiral conductor coil includes a plurality of first enlarged portionsalong a length thereof, the second spiral conductor coil includes aplurality of second enlarged portions along a length thereof, and eachof the second enlarged portions corresponds to and overlaps a respectiveone of the first enlarged portions. Each of the first enlarged portionsand each of the second enlarged portions may be disk-shaped. Also, themulti-layer cylindrical wireless energy transfer cell may furtherinclude a ferrite core provided inside the inner cylindrical insulator.

Therefore, it should now be apparent that the invention substantiallyachieves all the above aspects and advantages. Additional aspects andadvantages of the invention will be set forth in the description thatfollows, and in part will be obvious from the description, or may belearned by practice of the invention. Moreover, the aspects andadvantages of the invention may be realized and obtained by means of theinstrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description given below, serve to explain the principles ofthe invention. As shown throughout the drawings, like reference numeralsdesignate like or corresponding parts.

FIG. 1 is a block diagram of a wireless energy transfer system accordingto one embodiment of the present invention;

FIG. 2 is a block diagram of an embodiment of a general wireless energytransfer unit that may be employed in, for example, the system of FIG.1;

FIGS. 3A, 3B and 3C are top plan, side elevational and cross-sectionalviews, respectively, of one particular embodiment of a wireless energytransfer cell that may be employed in the wireless energy transfer unitsdescribe herein;

FIG. 3D is a simplified equivalent circuit model of a version of thewireless energy transfer cell shown in FIGS. 3A-3C;

FIGS. 4A, 4B and 4C are top plan, side elevational and cross-sectionalviews, respectively, of another particular embodiment of a wirelessenergy transfer cell that may be employed in the wireless energytransfer units describe herein;

FIG. 4D is a simplified equivalent circuit model of a version of thewireless energy transfer cell shown in FIGS. 4A-4C;

FIGS. 5A and 5B are top plan and side elevational views, respectively,of another particular embodiment of a wireless energy transfer cell thatmay be employed in the wireless energy transfer units describe herein;

FIG. 5C is a simplified equivalent circuit model of a version of thewireless energy transfer cell shown in FIGS. 5A-5B;

FIGS. 6, 7 and 8 are top plan views of flat, thin film wireless energytransfer cells according to further alternative embodiments;

FIGS. 9 and 10 are isometric views of cylindrical wireless energytransfer cells according to still further alternative embodiments;

FIG. 11A is an exploded view and FIG. 11B is a top plan view of aparticular embodiment of the transmitter wireless energy transfer unitshown in FIG. 1 in which the capacitance of the LC resonant tank, andtherefore the resonant frequency, may be selectively adjusted;

FIG. 12 is an exploded view of a particular embodiment of the receiverwireless energy transfer unit shown in FIG. 1 in which the inductance ofthe LC resonant tank, and therefore the resonant frequency, may beselectively adjusted;

FIGS. 13 and 14 are block diagrams of wireless energy transfer relaysystems according to alternative embodiments of the present invention;

FIGS. 15A and 15B are a block diagrams of wireless energy transfersensor networks according to two different embodiments of the presentinvention;

FIG. 16 is an exploded view of a wireless energy transfer unit having avertical cell design according to an alternative embodiment of thepresent invention;

FIG. 17 is an exploded view of a wireless energy transfer unit having ahorizontal cell design according to a further alternative embodiment ofthe present invention;

FIG. 18 is a top plan view of an alternative coil that may be used inthe wireless energy transfer unit of FIG. 17;

FIG. 19 is an isometric view of a non-coil wireless energy transfer cellaccording to still a further alternative embodiment;

FIG. 20 is an exploded isometric view of a multi-layer wireless energytransfer cell according to still another alternative embodiment;

FIG. 21 is a top plan view of the disk-shaped coil element of themulti-layer wireless energy transfer cell shown in FIG. 20; and

FIG. 22 is partially cut-away top plan view of a cylindrical wirelessenergy transfer cell according to a further alternative embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Directional phrases used herein, such as, for example and withoutlimitation, top, bottom, left, right, upper, lower, front, back, andderivatives thereof, relate to the orientation of the elements shown inthe drawings and are not limiting upon the claims unless expresslyrecited therein.

As employed, herein, the statement that two or more parts or componentsare “coupled” together shall mean that the parts are joined or operatetogether either directly or through one or more intermediate parts orcomponents.

As employed herein, the statement that two or more parts or components“engage” one another shall mean that the parts exert a force against oneanother either directly or through one or more intermediate parts orcomponents.

As employed herein, the term “number” shall mean one or an integergreater than one (i.e., a plurality).

FIG. 1 is a block diagram of a wireless energy transfer system 2according to one embodiment of the present invention. As described ingreater detail elsewhere herein, the wireless energy transfer system 2allows energy for use in providing power and/or data communications tobe transferred wirelessly from a source to a load based on the conceptof evanescent resonant coupling mediated through the overlap of thenonradiative near (e.g., magnetic) fields of two resonators (referred toas nonradiative resonant coupling). In particular, in the schemeemployed by the wireless energy transfer system 2, the coupling is notimplemented using the lossy radiative far-field, but rather isimplemented using the evanescent non-lossy stationary near-field.

Referring to FIG. 1, the wireless energy transfer system 2 includes anRF signal generator 4 operatively coupled to a power amplifier 6. The RFsignal generator 4 generates an RF energy signal 8, which is amplifiedby the power amplifier 6 to produce amplified RF energy signal 10. Thewireless energy transfer system 2 also includes a first wireless energytransfer unit 12 a acting as an energy transmitter and a second wirelessenergy transfer unit 12 b separated from the first wireless energytransfer unit 12 a and acting as a receiver. The first wireless energytransfer unit 12 a and the second wireless energy transfer unit 12 b aredescribed in greater detail elsewhere herein and have the same resonantfrequency or frequencies. A load 14 is operatively coupled to the secondwireless energy transfer unit 12 b for receiving RF energy 16 (in theone or more resonant frequencies) therefrom.

In operation, as shown schematically in FIG. 1, the first wirelessenergy transfer unit 12 a receives the amplified RF energy signal 10 andin response thereto and in a manner described elsewhere herein, causesRF energy 18 to be wirelessly transmitted between the first wirelessenergy transfer unit 12 a and the second wireless energy transfer unit12 b in the evanescent non-lossy stationary near-field. In response toreceiving the RF energy 18 and in a manner described elsewhere herein,the second wireless energy transfer unit 12 b outputs RF energy 16,which is received by the load 14. In one embodiment, the load 14includes a rectifier for converting the received RF energy 16 to DCpower for powering the load (as described elsewhere herein, the RFenergy 18 may have multiple frequencies and as a result may also includecommunication information).

FIG. 2 is a block diagram of an embodiment of a general wireless energytransfer unit 12 that may be used for the first wireless energy transferunit 12 a and the second wireless energy transfer unit 12 b. As seen inFIG. 2, the wireless energy transfer unit 12 includes a wireless energytransfer cell 20, a number of particular embodiments of which aredescribed herein, that is magnetically coupled to an energycoupling/extraction coil 22 comprising a conductor formed into one ormore loops, and can include a single loop or a continuous series ofloops. The wireless energy transfer cell 20 includes a single ormultiple LC resonant tanks having one or more conductors coupled to aninsulator. As noted above, the wireless energy transfer unit 12 canfunction as either a transmitter or a receiver. When functioning as atransmitter, RF energy (or some other form of energy, such as, withoutlimitation, another form of electromagnetic wave energy) of a particularfrequency or frequencies is applied to the energy coupling/extractioncoil 22 by, for example, a wired connection. The applied RF energy,through magnetic coupling between the energy coupling/extraction coil 22and the wireless energy transfer cell 20, causes RF energy of the sameparticular frequency or frequencies to be induced in and radiated by thewireless energy transfer cell 20, and in particular the LC resonant tankor tanks thereof. When functioning as a receiver, the wireless energytransfer cell 20 will receive RF energy of a particular frequency orfrequencies, as determined by the resonance properties of the LCresonant tank or tanks thereof The received RF energy (which is presentin the area surrounding the wireless energy transfer cell 20), throughmagnetic coupling between the wireless energy transfer cell 20 and theenergy coupling/extraction coil 22, causes RF energy of the sameparticular frequency or frequencies to be induced in the energycoupling/extraction coil 22 that is present in the area surrounding thewireless energy transfer cell 20. That RF energy may be transmitted to aload, such as load 14, by making an appropriate connection to the energycoupling/extraction coil 22.

FIGS. 3A and 3B are top plan and side elevational views, respectively,of one particular embodiment of a wireless energy transfer cell 20-3.FIG. 3C is a cross-sectional view of the wireless energy transfer cell20-3 taken along lines C-C of FIG. 3A. As described in greater detailbelow, the wireless energy transfer cell 20-3 is a thin film cell designthat, in a situation where it is used to function as a receiver asdescribed elsewhere herein, can be imbedded, or imprinted, on theexterior or interior cover (or container) of another device (e.g., theload 14). The particular design in FIGS. 3A-3C not only utilizes themaximum dimensions of the associated (parent) device to capture themagnetic flux produced by the distally located transmitter wirelessenergy transfer unit 12, but also takes no interior space of theassociated (parent) device. In the particular embodiment shown in FIGS.3A-3C, the wireless energy transfer cell 20-3 is circular (cylindrical)in shape in order to correspond to an associated (parent) device that iscircular (cylindrical) in shape. It is to be understood that this ismeant to be exemplary only, and that the wireless energy transfer cell20-3 may take on other shapes (e.g., rectangular) in order to correspondto associated (parent) devices of other shapes.

As seen in FIGS. 3A-3C, the wireless energy transfer cell 20-3 includesthree layers. The interior layer is an insulator layer 24 made of, forexample and without limitation, a polymer. The insulator layer 24 servesas an insulator between the conductive exterior and interior layersdescribed below. The exterior layer is a helical conductor coil 26surrounding and coupled to the outer surface of the insulator layer 24.The helical conductor coil 26 forms an inductor which captures andgenerates the magnetic field. The interior layer includes a number ofconductive strips 28 spaced around and coupled to the inner surface ofthe insulator layer 24 in an orientation that is generally parallel withthe central axis of the wireless energy transfer cell 20-3. Theconductive strips 28 form physical capacitors with the overlapped partsof the helical conductor coil 26 and divide the inductor formed by thehelical conductor coil 26 into equal or unequal segments. Thus, thedesign of the wireless energy transfer cell 20-3 forms a compact LC tankcircuit with no wire connections.

In order to reduce the weight and increase the pliability of thewireless energy transfer cell 20-3, the helical conductor coil 26 andthe conductive strips 28 are in one specific implementation made ofcopper tape or another similar suitable conductive material. Also, thehelical conductor coil 26 and/or the conductive strips 28 may have alarge surface area thereof plated with silver in order to provide forsmall electrical resistance adapting to the skin effect of RF current.

In the particular embodiment of the wireless energy transfer cell 20-3,each conductive strip 28 covers all turns of the helical conductor coil26 and provides connections for those capacitors that it forms.Different turns of the helical conductor coil 26 are then connectedthrough the capacitors in the same strip, which configuration constructsresonance loops. As a result, the wireless energy transfer cell 20-3forms a structure with multiple resonant frequencies. Thus, the wirelessenergy transfer cell 20-3 is able to simultaneously form both energytransfer channel or channels for power transmission and data transferchannel or channels for information exchange. For efficient energytransfer, the radius of the wireless energy transfer cell 20-3 and thenumber of turns of the helical conductor coil 26 should be designed sothat the wireless energy transfer cell 20-3 can receive or emit adesired amount of energy. In addition, the number of the conductivestrips 28 and their locations must be determined to form transmissionchannels within the frequency range or ranges of interest. Also, thewidth of the conductive strips 28 must be selected to obtain the desiredresonant frequencies.

FIG. 3D is a simplified equivalent circuit model 30 of a version of thewireless energy transfer cell 20-3 (losses are not taken intoconsideration). For simplicity, the circuit includes only two loops inthe helical conductive coil 26 and three conductive strips 28. Thesegment of a part of the strips in both the exterior and interior layerscan be modeled as a transmission line whose equivalent circuit is aT-circuit as indicated by impedance

$\frac{Z_{1}}{2}$and admittance Y. Z₂ is the impedance of the part without a strip at theinterior layer. The impedances and the admittance are calculated usingthe following equations:

$\begin{matrix}{\frac{Z_{1}}{2} = {\frac{Z_{l}}{2}\frac{\tanh\left( {l_{1}{\sqrt{Z_{l}Y_{l}}/2}} \right)}{\sqrt{Z_{l}Y_{l}}/2}}} & (1) \\{Y = {Y_{l}\frac{\sinh\left( {l_{1}\sqrt{Z_{l}Y_{l}}} \right)}{\sqrt{Z_{l}Y_{l}}}}} & (2) \\{{Z_{2} = {Z_{l}l_{2}}},} & (3)\end{matrix}$where Z₁, Y₁ are the impedance per unit length and admittance per unitlength of the transmission line model, and l₁ and l₂ are the lengths ofthe segment with strips in both layers and the distance between twostrips in the interior layer. In the above equations, the inductance inthe interior layer of each segment is neglected since it is much smallerthan that in the exterior layer, and therefore the distributedimpedances are the same in each segment.

Mesh current analysis is used to solve the circuit. The left and rightloops are symmetric and therefore only two mesh equations are needed.Denoting I₁ and I₂ as the mesh currents of the left loop and the middleloop, respectively, we have:

${I_{1} = \frac{V\left( {{2Z_{C}} + Z_{L}} \right)}{2\left( {{2Z_{L}^{2}} + {7Z_{L}Z_{C}} + {2Z_{C}^{2}}} \right)}},{and}$${I_{2} = \frac{{VZ}_{C}}{{2Z_{L}^{2}} + {7Z_{L}Z_{C}} + {2Z_{C}^{2}}}},$where Z_(L)=Z₁+Z₂,

$Z_{C} = \frac{1}{Y}$and V is the voltage around the loop induced by the external field.

By setting I₁=∞ and I₂=∞, we get the condition for the circuitresonating:

$\begin{matrix}{{\left( {Z_{1} + Z_{2}} \right)Y} = {\frac{{- 7} \pm \sqrt{33}}{4}.}} & (4)\end{matrix}$

By replacing the parameters in (4) with the parameters in (1)-(3), theresonant condition becomes

$\begin{matrix}{{\left( {{Z_{l}\frac{\tanh\left( {l_{1}{\sqrt{Z_{l}Y_{l}}/2}} \right)}{\sqrt{Z_{l}Y_{l}}/2}} + {Z_{l}l_{2}}} \right)Y_{l}\frac{\sinh\left( {l_{1}\sqrt{Z_{l}Y_{l}}} \right)}{\sqrt{Z_{l}Y_{l}}}} = \frac{{- 7} \pm \sqrt{33}}{4}} & (5)\end{matrix}$

Since Z_(l)=jωL_(l) and Y_(l)=jωC_(l), where L_(l) and C_(l) are thedistributed inductance and capacitance, we can use equation (5) todetermine the resonant frequency if the size of the design is provided.Conversely, if the resonant frequency is selected, we can determine thesize of the design. There does not exist an analytical solution todetermine resonant frequencies from Eq. (5). However, we can do sonumerically, such as using the finite element method. As we can see fromEq. (5), there are at least two resonant frequencies in the circuit(observing the plus and minus signs to the right side). Again, it shouldbe noted that the solution in (5) is for a special case only (two loopson the exterior and three strips in the interior). The inventors havenot obtained a general solution for the circuit with an arbitrary numberof loops and strips. However, the inventors predict that, by increasingthe number of loops and strips, more resonant frequencies will bepresent.

FIGS. 4A and 4B are top plan and side elevational views, respectively,of an alternative particular embodiment of a wireless energy transfercell 20-4 that is similar to the wireless energy transfer cell 20-3.FIG. 4C is a cross-sectional view of the wireless energy transfer cell20-4 taken along lines C-C of FIG. 4A. In the wireless energy transfercell 20-4, the conductive strips 28 each cover only two adjacentportions of the helical conductor coil 26. Furthermore, in either thewireless energy transfer cell 20-3 or the wireless energy transfer cell20-4, the rectangular conductive strips 28 can be replaced by conductivestrips having other patterns or shapes arranged in different ways forparticular applications. The design of the wireless energy transfer cell20-4 which includes a larger number of conductive strips 28 helps tobetter distribute the capacitance over the interior surface whilereducing the eddy current.

FIG. 4D is a simplified equivalent circuit model 32 of a version of thewireless energy transfer cell 20-4 using a Π-circuit model. Theimpedances and admittance of each segment in FIG. 4D are represented bythe same symbols as those in FIG. 3D. Here it is also assumed that thelength of a segment having part of the conductors in both layers issmall enough so that the inductance of the conductor in the interiorlayer can be neglected. In the Π-circuit model, the impedances and theadmittance are calculated using the following equations:

$\begin{matrix}{Z_{1} = {Z_{l}\frac{\sinh\left( {l_{1}\sqrt{Z_{l}Y_{l}}} \right)}{\sqrt{Z_{l}Y_{l}}}}} & (6) \\{\frac{Y}{2} = {\frac{Y_{l}}{2}\frac{\tanh\left( {l_{1}{\sqrt{Z_{l}Y_{l}}/2}} \right)}{\sqrt{Z_{l}Y_{l}}/2}}} & (7) \\{{Z_{2} = {Z_{l}l_{2}}},} & (8)\end{matrix}$

It is obvious that when the circuit is resonating, the current stays inthe loops indicated by the arrows. There are no currents flowing intothe inductors with the impedances of Z₂ since they are not in a closedloop. To find the resonant frequency, we calculate the total impedanceof the circuit

$\begin{matrix}{{Z_{total} = {\frac{4N_{1}Z_{1}}{{Z_{1}Y} + 4} + {N_{2}Z_{2}}}},} & (9)\end{matrix}$where N₁ and N₂ are the total lengths of the segments with conductors inboth layers and only in the exterior layer separately. By settingZ_(total)=∞, the resonant condition can be found. Using the distributedparameters in (6) and (7), the simplified equation below can be found:sin h(l ₁√{square root over (Z ₁ Y)})tan h(l ₁√{square root over (Z ₁Y)}/2)=−2.  (10)The solution of equation (10) is:l ₁√{square root over (Z ₁ Y)}=j(2k+1)π,k=0,1,2, . . .  (11)Now using the distributed inductance and capacitance instead of theimpedance and admittance in (11), the resonant frequency may be found:

$\begin{matrix}{{\omega = \frac{\left( {{2k} + 1} \right)\pi}{l_{1}\sqrt{L_{l}C_{l}}}},{k = 0},1,2,\ldots} & (12)\end{matrix}$Equation (12) indicates that there are many resonant frequencies in thisdesign. These frequencies can be useful for many purposes. For instance,the lower frequencies can be used to transmit energy for power while thehigher frequencies can be used for communication. If the loss by addinga distributed resistance per length R_(l) of the Π-circuit (the loss inthe insulator is neglected) is considered, the Q factor then becomes

$\begin{matrix}{{Q = {\frac{\omega\; L_{l}}{R_{l}} = {\frac{\left( {{2k} + 1} \right)\pi}{l_{1}R_{l}}\sqrt{\frac{L_{l}}{C_{l}}}}}},{k = 0},1,2,\ldots} & (13)\end{matrix}$Note that one segment of the interior layer does not have an inductorbut does have an equivalent resistor, so the Q factor is reduced by 2.

FIGS. 5A and 5B are top plan and side elevational views, respectively,of a wireless energy transfer cell 20-5 according to another particularembodiment. Like the wireless energy transfer cell 20-3 and the wirelessenergy transfer cell 20-4, the wireless energy transfer cell 20-5 is athin film cell design that, in a situation where it is used to functionas a receiver as described elsewhere herein, can be imbedded, orimprinted, on the exterior or interior cover (or container) of anotherdevice (e.g., the load 14). The particular design in FIGS. 5A and 5B notonly utilizes the maximum dimensions of the associated (parent) deviceto capture the magnetic flux produced by the distally locatedtransmitter wireless energy transfer unit 12, but also takes no interiorspace of the associated (parent) device. In the particular embodimentshown in FIGS. 5A and 5B, the wireless energy transfer cell 20-5 isrectangular in shape in order to correspond to an associated (parent)device that is rectangular (cross section) in shape. It is to beunderstood that this is meant to be exemplary only, and that thewireless energy transfer cell 20-5 may take on other shapes (e.g.,circular/cylindrical) in order to correspond to associated (parent)devices of other shapes. As described below, the design of the wirelessenergy transfer cell 20-5 forms a compact LC tank circuit with no wireconnections.

As seen in FIGS. 5A and 5B, the wireless energy transfer cell 20-5includes three layers. The interior layer is an insulator layer 24 asdescribed elsewhere herein. The exterior layer is a conductor coil 34surrounding and coupled to the exterior surface of the insulator layer24, and the interior layer is a conductor coil 36 coupled to theinterior surface of the insulator layer 24. The conductor coil 34 andthe conductor coil 36 are positioned such that they overlap andcorrespond to one another as they wind around the respective surfaces ofthe insulator layer 24. As a result, the capacitance produced by theconductor coil 34 and the conductor coil 36 (and the LC tank formed bythe wireless energy transfer cell 20-5) is able to be increased relativeto what is possible with similarly sized wireless energy transfer cells20-3 and 20-4 due to the fact that the entire surface of the conductorcoil 34 and the conductor coil 36 is used to create a capacitor. Inorder to perfectly align the conductor coil 34 and the conductor coil 36on both sides of the insulator layer 24, stair-like conductor patternsare utilized as shown in FIG. 5B. In addition, as seen in FIGS. 5A and5B, the conductor coil 34 is connected to the conductor coil 36 by aconductive patch 38. This results in the what is equivalent to a singlecoil having an inductance that is approximately double the inductancethat would be produced by the conductor coil 34 and conductor coil 36individually. The ability to increase the capacitance and inductance asjust described is advantageous as it allows certain desired resonancefrequencies to be obtained in a wireless energy transfer cell 20-5 thatcould not be obtained by similarly sized wireless energy transfer cells20-3 and 20-4. Thus, a wireless energy transfer cell 20-5 may be able tobe made small enough to accommodate a relatively small parent devicewhile still achieving the particular desired resonant frequency wheresimilarly sized wireless energy transfer cells 20-3 and 20-4 would notbe able to do so.

In order to reduce the weight and increase the pliability of thewireless energy transfer cell 20-5, the conductor coil 34 and theconductor coil 36 are in one specific implementation made of copper tapeor another similar suitable conductive material. Also, the conductorcoil 34 and/or the conductor coil 36 may have a large surface areathereof plated with silver in order to provide for small electricalresistance adapting to the skin effect of RF current.

FIG. 5C is an equivalent circuit 40 of the wireless energy transfer cell20-5 using a Π-circuit. In the equivalent circuit 40, Z₁ and Y/2 are thesame as those defined in Eqs. (6) and (7). The resonant condition nowbecomes Z₁Y=−2 which leads tosin h(l√{square root over (Z ₁ Y)})tan h(l√{square root over (Z ₁Y)}/2)=−1,  (14)where in this design l is the length of the conductor in the exteriorlayer. The solution to Eq. (14) is

$\begin{matrix}{{{l\sqrt{Z_{1}Y}} = {j\frac{\left( {{2k} + 1} \right)\pi}{2}}},{k = 0},1,2,\ldots} & (15)\end{matrix}$Using the distributed inductance and capacitance instead of theimpedance and admittance in equation (15), the resonant frequency isfound:

$\begin{matrix}{{\omega = \frac{\left( {{2k} + 1} \right)\pi}{2l\sqrt{L_{l}C_{l}}}},{k = 0},1,2,\ldots} & (16)\end{matrix}$It is seen that the frequencies of this design are lower than those ofthe wireless energy transfer cell 20-3 if the distributed parameters arethe same. With these resonant frequencies, resonant objects withmultiple purposes can be designed. The Q factor of this design is

$\begin{matrix}{{Q = {\frac{\omega\; L_{l}}{R_{l}} = {\frac{\left( {{2k} + 1} \right)\pi}{2l\; R_{l}}\sqrt{\frac{L_{l}}{C_{l}}}}}},{k = 0},1,2,\ldots} & (17)\end{matrix}$

In the wireless energy transfer cells 20-3, 20-4 and 20-5 describedpreviously, a magnetic core can be used inside the cell to increaseinductance or the Q-factor. This core can also be excited actively by acurrent in a certain frequency or frequencies in order to produce a biasmagnetic field, a communication signal, or an excitation to the resonantsystem.

FIG. 6 is a top plan view of a flat, thin film wireless energy transfercell 20-6 that forms a compact LC tank circuit with no wire connectionsaccording to a further alternative embodiment. The wireless energytransfer cell 20-6 includes three layers. The middle layer is aninsulator layer 42 made of, for example and without limitation, apolymer. The insulator layer 42 serves as an insulator between theconductive top and bottom layers described below. The top layer is asquare spiral conductor coil 44 coupled to the top surface of theinsulator layer 42. The conductor coil 44 forms an inductor whichcaptures and generates the magnetic field (i.e., it will both receiveand transmit energy from and to another energy transfer cell (resonantenergy exchange)), regardless of whether it is used on the input or loadside. The bottom layer includes a number of conductive strips 46 spacedaround and coupled to the bottom surface of the insulator layer 42. Theconductive strips 46 form physical capacitors with the overlapped partsof the conductor coil 44 and divide the inductor formed by the conductorcoil 44 into segments.

FIG. 7 is a top plan view of a flat, thin film wireless energy transfercell 20-7 that forms a compact LC tank circuit with no wire connectionsaccording to still a further alternative embodiment. The wireless energytransfer cell 20-7 includes three layers. The middle layer is aninsulator layer 48 made of, for example and without limitation, apolymer. The insulator layer 48 serves as an insulator between theconductive top and bottom layers described below. The top layer is acircular spiral conductor foil 50 coupled to the top surface of theinsulator layer 48. The conductor foil 50 forms an inductor whichcaptures and generates the magnetic field (i.e., it will both receiveand transmit energy from and to another energy transfer cell (resonantenergy exchange), regardless of whether it is used on the input or loadside. The bottom layer includes a number of conductive strips 52 spacedaround and coupled to the bottom surface of the insulator layer 48. Theconductive strips 52 form physical capacitors with the overlapped partsof the conductor foil 50 and divide the inductor formed by the conductorfoil 50 into segments.

FIG. 8 is a top plan view of a flat, thin film wireless energy transfercell 20-8 that forms a compact LC tank circuit with no wire connectionsaccording to yet a further alternative embodiment. The wireless energytransfer cell 20-8 includes three layers. The middle layer is aninsulator layer 54 made of, for example and without limitation, apolymer. The insulator layer 54 serves as an insulator between theconductive top and bottom layers described below. The top layer is asquare spiral conductor coil 56 coupled to the top surface of theinsulator layer 54. As seen in FIG. 8, the square spiral conductor coil56 includes crisscrossing portions 60 along the length thereof such thatthe beginning 62 and the end 64 of the continuous square spiralconductor foil 50 are positioned adjacent to one another. The conductorcoil 56 forms an inductor which captures and generates the magneticfield (i.e., it will both receive and transmit energy from and toanother energy transfer cell (resonant energy exchange)), regardless ofwhether it is used on the input or load side. The bottom layer includesa number of conductive strips 58 spaced around and coupled to the bottomsurface of the insulator layer 54. The conductive strips 58 formphysical capacitors with the overlapped parts of the conductor coil 56and divide the inductor formed by the conductor coil 56 into segments.

FIG. 9 is an isometric view of a wireless energy transfer cell 20-9 thatforms a compact LC tank circuit with no wire connections according toyet a further alternative embodiment. The wireless energy transfer cell20-9 is similar to the wireless energy transfer cell 20-3 shown in FIGS.3A-3C, except that the wireless energy transfer cell 20-9 includes ahelical conductor coil 26′ that is slightly different than the helicalconductor coil 26. Specifically, the helical conductor coil 26′ includescrisscrossing portions 66 along the length thereof such that thebeginning 68 and the end 70 of the continuous helical conductor coil 26′are positioned adjacent to one another.

FIG. 10 is an isometric view of a wireless energy transfer cell 20-10that forms a compact LC tank circuit with no wire connections accordingto yet a further alternative embodiment. The wireless energy transfercell 20-10 is similar to the wireless energy transfer cell 20-5 shown inFIGS. 5A and 5B, except that the wireless energy transfer cell 20-10 iscircular/cylindrical (although it could also be rectangular or anothersuitable shape) and includes helical conductor coils 34′ and 36′ thatare slightly different than the conductor coils 34 and 36 of FIGS. 5Aand 5B. Specifically, the helical conductor coils 34′ and 36′ eachinclude crisscrossing portions 72 along the length thereof such that thebeginning and the end of the continuous helical conductor coils 34′ and36′ are positioned adjacent to one another (and possibly connected toone another).

In order to reduce the weight and increase the pliability of thewireless energy transfer cells 20-6, 20-7, 20-8, 20-9 and 20-10, theconductor coils and/or conductive strips thereof may be made of coppertape or another similar suitable material. Also, the conductor coilsand/or conductive strips may have a large surface area thereof platedwith silver in order to provide for small electrical resistance adaptingto the skin effect of RF current.

FIG. 11A is an exploded view and FIG. 11B is a top plan view of aparticular embodiment of the transmitter wireless energy transfer unit12 a shown in FIG. 1, identified in FIGS. 11A and 11B as wireless energytransfer unit 12 a-11 (it should be noted, however, that the wirelessenergy transfer unit 12 a-11 may also be used as a receiver). Asdescribed in greater detail below, the wireless energy transfer unit 12a-11 is structured such that the resonant frequency of the wirelessenergy transfer cell 20 formed therein is selectively adjustable byselectively adjusting the capacitance thereof. The wireless energytransfer unit 12 a-11 includes an energy coupling/extraction coil 22 inthe form of a single loop conductor which transmits energy to thewireless energy transfer cell 20 by magnetic coupling as describedelsewhere herein. The wireless energy transfer cell 20 in thisparticular embodiment includes a helical coil 74 having a first end 76and a second end 78 and an adjustable capacitor 80. The helical coil 74is, in one specific, non-limiting embodiment, made of a copper pipecoated with epoxy for insulation. The adjustable capacitor 80 includesconcentric insulator rings 82 (outer) and 84 (inner), made of a polymeror some other suitable electrical insulating material, that are able torotate and shift relative to one another as indicated by the arrows inFIG. 11A. A first conductor sheet 86, made of, for example, copper foilor another suitable conducting material, is coupled to the exteriorsurface of the concentric insulator ring 82 and covers approximately 50%thereof. A second conductor sheet 88, made of, for example, copper foilor another suitable conducting material, is coupled to the interiorsurface of the concentric insulator ring 84 and covers approximately 50%thereof When assembled, as seen in FIG. 11B, the adjustable capacitor 80is placed on top of the energy coupling/extraction coil 22, preferablywith an insulator, such as a sheet of insulating material, separatingthe two. In addition, the helical coil 74 is positioned inside theadjustable capacitor 80 and the first end 76 makes direct (andpreferably slideable) contact with the conductor sheet 86 and the secondend 78 makes direct (and preferably slideable) contact with theconductor sheet 88. This significantly reduces the resistance within theLC resonant tank circuit and eliminates the need for wire connectionsbetween the helical coil 74 and the adjustable capacitor 80. When theconcentric insulator rings 82, 84 shift relative to each other, thecapacitance varies over a magnitude of approximately four times for oneparticular embodiment of the adjustable capacitor 80, but could vary byother orders of magnitude depending on particular dimensions of theadjustable capacitor 80, providing adjustability of resonant frequencyof the wireless energy transfer unit 12 a-11.

FIG. 12 is an exploded view of a particular embodiment of the receiverwireless energy transfer unit 12 b shown in FIG. 1, identified in FIG.12 as wireless energy transfer unit 12 b-12 (it should be noted,however, that the wireless energy transfer unit 12 b-12 may also be usedas a transmitter). As described in greater detail below, the wirelessenergy transfer unit 12 b-12 is structured such that the resonantfrequency of the wireless energy transfer cell 20 formed therein isselectively adjustable by selectively adjusting the inductance thereof.The wireless energy transfer unit 12 b-12 includes an energycoupling/extraction coil 22 in the form of a helical conductor coilwhich extracts energy from the wireless energy transfer cell 20 thoughmagnetic coupling as described elsewhere herein so that the energy canbe provided to a load such as the load 14. The wireless energy transfercell 20 in this particular embodiment includes a helical coil 90 havinga first end 92 and a second end 94 and ring capacitor 96. The helicalcoil 90 is, in one specific, non-limiting embodiment, made of solidsilver wire in order to reduce resistance within the LC tank. The ringcapacitor 96 includes a cylindrical insulator ring 98 made of a polymeror some other suitable electrical insulating material. A first conductorring 100, made of, for example, silver sheet material (to reduceresistance within the LC tank) or another suitable conducting material,is coupled to the exterior surface of the insulator ring 98 and a secondconductor ring 102 made of, for example, silver sheet material (toreduce resistance within the LC tank) or another suitable conductingmaterial, is coupled to the interior surface of the insulator ring 96. Agap 104 is intentionally formed within both the first conductor ring 100and the second conductor ring 102 in order to break the potentiallyharmful loop current. When assembled, the helical coil 90 is positionedinside the ring capacitor 96 and the first end 92 makes direct contactwith the conductor ring 100 at point 106 and the second end 94 makesdirect contact with the conductor ring 102 at point 108. Thissignificantly reduces the resistance within the LC resonant tank circuitand eliminates the need for wire connections between the helical coil 90and the ring capacitor 96.

Since the ring capacitor 96 in this embodiment is not adjustable, it hasa fixed capacitance. Instead, the resonant frequency of the wirelessenergy transfer unit 12 b-12 is adjusted by changing the inductancevalue of the helical coil 90. This is achieved by placing aferromagnetic core 110 comprising a plurality of ferromagnetic discs 112at the center of the wireless energy transfer unit 12 b-12 within thehelical coil 90. In particular, the ferromagnetic core 110 is formed bystacking multiple ferromagnetic discs 112 which can be selectively addedor removed. As a result, the inductance value may be adjusted in aplurality of steps based on the number of ferromagnetic discs 112 thatare stacked.

As will be appreciated, in a system such as the wireless energy transfersystem 2, the wireless energy transfer unit 12 a will be larger(sometimes much larger) than the wireless energy transfer unit 12 b.However, as noted elsewhere herein, for the wireless energy transfersystem 2 to work, the resonant frequency or frequencies of the wirelessenergy transfer unit 12 a (transmitter) and the wireless energy transferunit 12 b (receiver) must be the same. The embodiment of the receiverwireless energy transfer unit 12 b-12 includes a number of attributesthat allow the LC product in the LC tank to be increased so that theresonant frequency can be matched to the resonant frequency of a largertransmitter wireless energy transfer unit 12 a. First, almost the entirecircumference of the ring capacitor 96 is utilized to maximizecapacitance. Also, the adjustable ferromagnetic core 110 allows theinductance of the helical coil 90 to be increased as needed.

The present inventors have found that multiple wireless energy transferunits 12 can be linked to form a relay system with much higher averageenergy transfer efficiency than that of the system activatedindividually. A block diagram of such a relay system 114 is shown inFIG. 13. By placing a single or a number of relay wireless energytransfer units 12 between the transmitter wireless energy transfer unit12 (leftmost in FIG. 13) and the receiver wireless energy transfer unit12 (rightmost in FIG. 13 and coupled to the load 14), the distance oftransfer can be extended significantly. A block diagram of analternative relay system 116 is shown in FIG. 14. In the alternativerelay system 116, the relay units are wireless energy transfer cells 20rather than wireless energy transfer units 12. As a further alternative,the relay units can be a combination of wireless energy transfer units12 and wireless energy transfer cells 20. In addition, the relay unitsneed not be positioned in a linear fashion with respect to one anotherand the transmitter and/or receiver units, but instead the presentinventors have found that one or more may be offset such that the pathfrom the transmitter wireless energy transfer unit 12 to the receiverwireless energy transfer unit 12 is not linear (in fact, it may haveportions that are perpendicular to one another). Furthermore, the relayunits need not be arranged in a straight or curved path, a number ofrelay units can form a two-dimensional or three-dimensional array withequal or unequal distances between units. This array embodiment allowsenergy and/or data to be routed in desirable paths within the arraybetween arbitrary energy transmitter (source) and receiver (sink) units.Besides passing energy as relays, when necessary, relay units can alsoconsume energy in order to perform certain functions, such as acting asan infrequently activated sensor.

This relay technique is valuable in the design of a sensor networkbecause, when all the receiver nodes in the network resonate at the samefrequency, the interactions among all member nodes of the networkincrease the average energy transfer efficiency. One such sensor network118 for use in connection with a human subject is shown in FIG. 15A. Thesensor network 118 includes a transmitter wireless energy transfer unit12-T worn around the waist of the subject 120 like a belt. An RF powersupply 122 is coupled to the energy coupling/extraction coil 22 of thetransmitter wireless energy transfer unit 12-T. The sensor network 118also includes a number of receiver wireless energy transfer units 12-Rworn around various parts of the body of the subject 120, such as thearms, legs and head. Each receiver wireless energy transfer unit 12-Rhas a sensor 124 coupled to the energy coupling/extraction coil 22thereof, powered by the transferred RF energy as described elsewhereherein, for sensing or detecting variousparameters/characteristics/signals relating to the subject. The sensors124 may be attached externally to the body of the subject 120 and/orimplanted within the body of the subject 120, and can include, withoutlimitation, a blood pressure sensor, an accelerometer, a temperaturesensor, an ECG sensor, a microphone and an SpO₂ sensor. As describedelsewhere herein, data may also be communicated between the transmitterwireless energy transfer unit 12-T and the various receiver wirelessenergy transfer units 12-R using the wireless energy transfer techniquesof the present invention.

In another embodiment shown in FIG. 15B, the sensor network 118′includes a transmitter wireless energy transfer unit 12-T worn aroundthe waist of the subject 120 like a belt. An RF power supply within unit122 is coupled to the energy coupling/extraction coil of the transmitterwireless energy transfer unit 12-T. The sensor network 118′ alsoincludes sensor nodes which include receiver wireless energy transfercells 20 in the form of wireless energy transfer cells 20-6, 20-7,and/or 20-8. These flat cells, integrated with or coupled to microsensors and energy coupling/extraction coils, can be pasted on theunderside of clothes, or affixed directly on the skin, to acquirephysiological or physical variables, such as multichannelelectrocardiograms for 24-hour heart monitoring or motion/positionsignals for body balance and physical activity monitoring. Noninvasiveor implantable devices embedded or imprinted with energy transfer cells(in a suitable form selected from 20-3 through 20-8) within or on thecover of the parent device can also be used as the sensor nodes of thebody sensor network 118′. Both the energy and data within the bodysensor network 118′ are centrally provided/collected by wireless energytransfer unit 12-T and RF power supply within unit 122. The collecteddata can be stored within unit 122 or transmitted wirelessly to acomputer located closely or remotely, with a possible connection to theInternet.

In another embodiment, the transmitter wireless energy transfer unit12-T is positioned in a stationary location, such as a headboard of abed or on a night stand, so that the sensors 124 can be powered and makemeasurements while the subject 120 is sleeping.

As noted in a number of places elsewhere herein, the techniques of thepresent invention may also be used for wireless data transfer. Althoughwireless data transfer can be a significant problem in a wide variety ofpractical applications such as microsensors and implantable devices, itsimplementation is relatively easy once the wireless power transfer asdescribed herein using a system such as the wireless energy transfersystem 2, the relay system 114 or 116, or the sensor network 118 isestablished. There are several methods to implement a communicationchannel taking advantage of an energy transfer channel as describedherein. For example, data can be sent by amplitude modulation (AM) ofthe energy transfer waveforms. They can also be sent by switching on oroff a constant amplitude energy transfer waveform signal(amplitude-shift keying, or ASK). In addition, as previously described,certain of the wireless energy transfer cells 20 (e.g., thin-filmdesigns 20-3, 20-4, 20-5) have multiple resonant frequencies and thusmay be used to implement multiple communication channels. Specifically,while one of these frequencies is used to transfer power, otherfrequencies can be used as communication channels, providing users withflexible design options.

FIG. 16 is an exploded view of wireless energy transfer unit 12-16having a vertical cell design according to an alternative embodiment.The wireless energy transfer unit 12-16 includes six cylindricalcomponents stacked in a concentric fashion forming a “pie” with verticallayers. The inner-most layer is an RF ferrite core 126. The next layeris a coil 128 preferably made of a strip of highly conductive (e.g.,silver) sheet wound in the spring-like form shown. The coil 128 has afirst end 130 and a second end 132. Preferably, the coil 128 is coatedwith a thin polymer film and compressed to form a low-height cylindricalcoil. This space-saving coil 128 is coupled with a ring capacitor 134,described below, at connection points 136. Specifically, the end 130 isdirectly coupled to one connection point 136 and the end 132 is coupledto the other connection point 136. A coil 138 comprises the energycoupling/extraction coil 22 of the wireless energy transfer unit 12-16.The coil 138 is preferably wound with thin, highly conductive (e.g.,copper) wire and glued into the shape of a cylindrical shell. The coil138 is magnetically coupled with the coil 128 to receive an appropriateamount of energy and output an AC current to a load such as the powersupply circuit of the parent device. The ring capacitor 134 includesinner and outer conductive (e.g., metal) rings 140, 142, respectively,preferably made of copper or gold films (or sheets) coupled on bothsides of a thin insulator (preferably polymer) sheet 144. In order toprevent an undesirable loop current within conductive rings 140, 142, agap 146 is made in each one to break this current. In this embodiment,the components other than the coil 138 form the wireless energy transfercell 20 of the wireless energy transfer unit 12-16. For ease ofillustration, certain components, e.g., insulating sheets betweencomponents such as between the coil 138 and the coil 128 and the ringcapacitor 134 to provide electrical isolation therebetween, are notshown in the Figure.

FIG. 17 is an exploded view of wireless energy transfer unit 12-17having a horizontal cell design according to a further alternativeembodiment. The wireless energy transfer unit 12-17 is designed in asandwich structure. The wireless energy transfer unit 12-17 includes acapacitor 148 formed by an insulator film 150, such as, withoutlimitation, a low-loss polymer or inorganic film, with conductive (e.g.,gold) films 152 attached to both sides (only one side is shown in FIG.17). Each conductive film 152 includes a connection tab 154. Thewireless energy transfer unit 12-17 also includes a planar coil 156having ends 158 on an insulating substrate (not shown). The two ends 158of the coil are directly connected to respective tabs 154 of the metalfilms 152, where one connection is at the center and the other is nearthe side. A coil 160 is also provided and comprises the energycoupling/extraction coil 22 of the wireless energy transfer unit 12-17.The coil 160 is structurally similar to the coil 156 but preferably hasmore turns. The coil 160 is magnetically coupled with the coil 156. Thetwo ends 162 of the coil 160 are energy input/output terminals. Finally,the wireless energy transfer unit 12-17 includes a polymer protectioncover 164 with two connection terminals 166 for coupling to the ends 162(see double arrows shown in FIG. 17). Again, one terminal 166 is locatedat the center and the other at the side. Preferably, the operatingfrequency of the wireless energy transfer unit 12-17 is intended to bebetween 10-30 MHz, although it can be lower or higher. In thisembodiment, the components other than the coil 160 form the wirelessenergy transfer cell 20 of the wireless energy transfer unit 12-17. Forease of illustration, certain components, e.g., additional insulatingsheets between components and additional protection covers, are notshown in the Figure.

It has been shown that the performance of the planar spiral coil 158 canbe improved considerably by using advanced thin-film technology. Forexample, as shown in FIG. 18, an alternative coil 156′ may be formed bymaking cross-connections 168 in the coil 156′, which results in asymmetric structure with ends 158 positioned adjacent to one another.This structure reduces the capacitive coupling within the coil 156′ andimproves quality factors. It has also been shown that this design can beextended to three dimensions with significantly better performance. Suchdesigns are shown in FIGS. 9 and 10.

In the various embodiments described herein (e.g., without limitation,FIGS. 3A-3C, 4A-4C, 5A-5B, 6-12 and 16-17), energy transfer (for powerand/or data transfer) is provided by the magnetic field in the freespace. In contrast, the electric field is confined within the physicalcapacitors (including the insulators) provided as part of the wirelessenergy transfer cells. This feature effectively prevents the leakage ofthe electrical field and helps reduce health concerns since the humanbody (and other electrically conductive objects) interacts much morestrongly with electric fields than with magnetic fields. The designsdescribed herein also improve efficiency because the power absorption byelectrically conductive objects is reduced. Further, in many of thedesigns, the wireless energy transfer cells can be made to be thin,soft, flexible and light.

FIG. 19 is an isometric view of a non-coil wireless energy transfer cell20-19 according to still a further alternative embodiment. The wirelessenergy transfer cell 20-19 comprises a laminated sheet that includesfive layers. Specifically, the wireless energy transfer cell 20-19includes a top layer 170 and a bottom layer 178 each made of amagneto-electric material that produces an electric field when exposedto a magnetic field. An example of a suitable, preferredmagneto-electric material, known as Metglas®, is described in J. Zhai,Z. Xing, S. Dong, J. Li and D. Viehland, “Magnetoelectric LaminateComposites: An Overview,” J. Am. Ceram. Soc., 91(2):351-358, 2008. Thewireless energy transfer cell 20-19 also includes conductor layers 172and 176 positioned adjacent to the top layer 170 and the bottom layer178, respectively. Each conductor layers 172 and 176 is made of aconducting material, such as a suitable metallic material, and forms anelectrode. A central layer 174 is located in between the conductorlayers 172 and 176. The central layer 174 is made of a piezoelectricmaterial. In operation, when a magnetic field is applied to the toplayer 170 and the bottom layer 178 as a result of the magnetic couplingwith the energy coupling/extraction coil as described herein, anelectric field is produced and applied to the conductor layers 172 and176. The conductor layers 172 and 176 then apply the electric field tothe central layer 174, causing it to resonate. The wireless energytransfer cell 20-19 may be preferred in certain applications since thevarious coil-capacitor structures described elsewhere herein have anumber of forms of energy loss due to electromagnetic radiation andelectrical resistance within the associated conductor, whereas theconversion between the magnetic and electric fields in the wirelessenergy transfer cell 20-19 tends to be more efficient (in some cases upto 100 times more efficient).

FIG. 20 is an exploded isometric view of a multi-layer wireless energytransfer cell 20-20 according to still another alternative embodiment.The wireless energy transfer cell 20-20 includes a number of disk-shapedcoil elements 180. A top plan view of the disk-shaped coil element 180is shown in FIG. 21. More specifically, the wireless energy transfercell 20-20 includes a top disk-shaped coil element 180A, a middledisk-shaped coil element 180B and a bottom disk-shaped coil element180C. A first insulator disk 182A is provided between the topdisk-shaped coil element 180A and the middle disk-shaped coil element180B, and a second insulator disk 182B is provided between the middledisk-shaped coil element 180B and the bottom disk-shaped coil element180C. Each insulator disk 182 is made of a suitable insulating material,such as, for example and without limitation, a polymer or a ceramicmaterial. In addition, as seen in FIG. 21, each disk-shaped coil element180 includes an insulator layer 184 made of a suitable insulatingmaterial, such as, for example and without limitation, a polymer or aceramic material, and a film coil 186 made of a conducting material suchas, without limitation, copper (or another suitable metal) film,provided on top of the insulating layer 184. The film coil 186 is formedby making cross-connections 188 in the film coil 186, which results in asymmetric structure with ends (terminals) 190 and 192 positionedadjacent to one another. The insulator layer 184 includes a firstconductive via 194 positioned adjacent to the end 190 of the film coil186 and a second conductive via 196 positioned adjacent to the end 192of the film coil 186. When assembled in a multi-layered, stackedfashion, a first conductive connector 198 electrically connects the end190 of the top disk-shaped coil element 180A to the end 192 of themiddle disk-shaped coil element 180B through the conductive via 194 ofthe top disk-shaped coil element 180A and a hole 200 provided in thefirst insulator disk 182A (this is shown in the exploded, dissembledview of FIG. 20). Similarly, a second conductive connector 202electrically connects the end 190 of the middle disk-shaped coil element180 b to the end 192 of the bottom disk-shaped coil element 180 cthrough the conductive via 194 of the middle disk-shaped coil element180B and a hole 204 provided in the second insulator disk 182B. The filmcoils 186 and the insulator disks 182 together form an LC resonant tankfor the multi-layer wireless energy transfer cell 20-20.

As noted above, by including the cross-connections 188 as shown, the twoends 190, 192 (terminals) of the film coil 186 are at the same location,which facilitates stacking the disk-shaped coil elements 180 and theinsulator disk 182 as described. Since all of the disk-shaped coilelements 180 are identical and the film coil 186 of each has a largesurface area, there are relatively large distributed capacitances acrossthe insulator disks 182A and 182B. Large capacitances are oftendesirable in small devices operating at a relatively low resonantfrequency. This embodiment is therefore particularly suitable for smalldevices, such as a medical implant within which this embodiment can beplaced on the inside surface of the hermetically sealed cover thereofwithout taking up significant additional space.

While the embodiment shown in FIGS. 20 and 21 includes disk-shaped coilelements 180, other configurations inducing just two disk-shaped coilelements 180 or four or more disk-shaped coil elements 180 (with theappropriate number of insulator disks 182) are also possible.

FIG. 22 is top plan view in progressive partial cut-away of acylindrical multi-layer wireless energy transfer cell 20-22 according toanother alternative embodiment. The wireless energy transfer cell 20-22includes an inner cylindrical insulator 210 made of a suitableinsulating material such as, without limitation, a ceramic material or apolymer material. An optional inner cylindrical ferrite core 212 may beprovided within the inner cylindrical insulator 210, in which case theinner cylindrical insulator 210 would be in the form of a hollowcylindrical shell. A first spiral conductor coil 214 is provided on thesurface of the inner cylindrical insulator 210 along the length thereof.The first spiral conductor coil 214 is preferably made of a conductivefilm such as, without limitation, a metal film like copper film. Thefirst spiral conductor coil 214 is oriented in either a positive angleor a negative angle with respect to the longitudinal axis of the innercylindrical insulator 210. The first spiral conductor coil 214 includesa plurality of enlarged portions 216, each preferably in the shape of adisk, provided along the length thereof at predetermined positions. Aninsulator layer 218 is provided on top of the first spiral conductorcoil 214 along the length of the wireless energy transfer cell 20-22.Preferably, the insulator layer 218 is in the form of an insulator film,such as a polymer film. A second spiral conductor coil 220 is providedon the surface of the insulator layer 218 along the length thereof. Thesecond spiral conductor coil 220, like the first spiral conductor coil214, is preferably made of a conductive film such as, withoutlimitation, a metal film like copper film. The second spiral conductorcoil 220 is electrically connected to the first spiral conductor coil214 and is oriented in either a positive angle or a negative angle withrespect to the longitudinal axis of the inner cylindrical insulator 210,wherein, as seen in FIG. 22, the angle (positive or negative) isopposite the angle of the first spiral conductor coil 214. The secondspiral conductor coil 220 includes a plurality of enlarged portions 222,each preferably in the shape of a disk, provided along the lengththereof at predetermined positions that correspond to and overlap thepositions of the enlarged portions 216 of the first spiral conductorcoil 214. Thus, the enlarged portions 216 and 220 are provided at thepoints where the first spiral conductor coil 214 and the second spiralconductor coil 220 overlay and cross over one another. As a result, theenlarged portions 216 and the enlarged portions 222, with the insulatorlayer 218 in between, form capacitors on the wireless energy transfercell 20-22. Those capacitors along with the first spiral conductor coil214 and the second spiral conductor coil 220 together form an LCresonant tank for the cylindrical multi-layer wireless energy transfercell 20-22.

When compared to a traditional solenoid coil, the cylindricalmulti-layer wireless energy transfer cell 20-22 has several importantproperties. First, because of the diagonal orientation of both the firstspiral conductor coil 214 and the second spiral conductor coil 220, amuch larger elliptic cross-section of the coils may be achieved ascompared to the circular cross section of the inner cylindricalinsulator 210. In addition, the differently oriented ellipticcross-sections of the first spiral conductor coil 214 and the secondspiral conductor coil 220 can respond to magnetic fluxes in alldirections effectively (see arrows B₁, B₂, and B₃ in FIG. 22). As aresult, the orientations of the transmitting and receiving wirelessenergy transfer cells (resonators) do not have to be aligned precisely.Depending on particular applications and operating frequencies, theinclusion of the inner cylindrical ferrite core 212 may allow for betterattraction of the magnetic field (this works better for lowerfrequencies). This embodiment is particularly suitable for poweringrod-shaped devices, such as, for example and without limitation, smallmedical implants like a muscle stimulator that can be implantedconveniently by injecting it into the body.

In all the wireless power transfer unit/cell designs previouslydescribed, the resonant frequency of the transmitter wireless powertransfer unit must be accurately tuned to that of the receiver wirelesspower transfer unit (or vice versa) in order to achieve the highestenergy transfer efficiency. Since the transmitter wireless powertransfer unit is typically located in the air, environmental factors,such as the room temperature and moisture, may cause a frequency drift.There may also be environmental factors affecting the stability of thereceiver wireless power transfer unit. Therefore, an automatic frequencyadjustment circuit may be desirable. In one particular embodiment, asystem employing wireless power transfer units as described herein isprovided with a frequency tuning function by using a variablecapacitance diode, which is a special diode in which the capacitance canbe electronically controlled (such diode are also commonly known asvaricaps or varactor diodes).

The present inventors have also studied two techniques to enhance energytransfer over a longer distance. The first technique uses a resonantigniter which initiates the coupling between the transmitter wirelesspower transfer unit and receiver wireless power transfer unit (thedynamic transition of the system has been described previously). The useof the resonant igniter can establish a wireless path of energy transfermore quickly because it sets the initial conditions of the energytransfer system closer to its steady state. The igniter can beimplemented by a phase-regulated amplifier which receives and amplifiesthe signal from the transmitter wireless power transfer unit. Theamplified signal drives the LC resonant tank of the receiver wirelesspower transfer unit into oscillation which is then enhancedprogressively by a positive feedback circuit until a full-scaleresonance is achieved between the transmitter wireless power transferunit and receiver wireless power transfer unit. Once the resonanttransmission path is fully established, the igniter is temporallydisengaged from the system and the receiver wireless power transfer unitstarts to receive energy with the established transmission path. In asystem with little loss, the established link is enough to keep thesystem resonating. If losses in the system are too high, the ignitioncircuit can be re-activated to reignite the transmission path. In thelatter case, the ignition circuit starts automatically after a certainperiod of time or after a certain energy level is detected. The cyclesof activation-reception repeat continuously during operation.

The second technique to increase the range of energy transfer is byusing an excitation circuit. This technique is similar to that utilizedin power stations. It is used to establish a strong magnetic fieldwithin the power generator to increase power generating efficiencyalthough excitation itself actually spends power. In the wireless powertransfer system, part of the received power is spent to establish astrong, constant oscillation within the LC resonant tank of the receiverwireless power transfer unit, which enhances the power transmission pathto the transmitter wireless power transfer unit, enabling the receiverwireless power transfer unit to draw more power from the transmitterwireless power transfer unit. The strength of excitation is optimallyadjusted so that the net energy, which equals the energy received minusthe energy spent, is higher than that without using excitation, and ismaximized.

Both the frequency tuning and igniting circuits can be implementedwithin the wireless power transfer unit or cell or the parent device.These circuits are powered by the power source within the parent device.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,deletions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as limited by theforegoing description but is only limited by the scope of the appendedclaims.

What is claimed is:
 1. A wireless energy transfer unit having at leastone resonant frequency, comprising: an energy coupling/extraction coil;and a wireless energy transfer cell magnetically coupled to said energycoupling/extraction coil, said wireless energy transfer cell comprisingan LC resonant tank including at least one insulator having a firstsurface and a second surface opposite said first surface, a spiralconductor coil provided on said first surface of said at least oneinsulator, and a plurality of non-spiral conductive strips provided, onsaid second surface of said at least one insulator, wherein said spiralconductor coil, said at least one insulator and said plurality ofnon-spiral conductive strips form at least one capacitor of said LCresonant tank.
 2. The wireless energy transfer unit according to claim1, wherein said energy coupling/extraction coil comprises a single loopcoil.
 3. The wireless energy transfer unit according to claim 1, whereinsaid energy coupling/extraction coil comprises a plurality of loops. 4.The wireless energy transfer unit according to claim 1, wherein each ofsaid non-spiral conductive strips overlaps a plurality of turns of saidspiral conductor coil.
 5. The wireless energy transfer unit according toclaim 4, wherein said at least one insulator is a cylindrical insulator,wherein said conductor coil is a helical conductor coil.
 6. The wirelessenergy transfer unit according to claim 5, wherein each of saidconductive strips covers only two adjacent portions of said helicalconductor coil.
 7. The wireless energy transfer unit according to claim1, wherein said at least one insulator is a flat insulator, wherein saidspiral conductor coil is a flat conductor coil and wherein each of saidplurality of non-spiral conductive strips is a flat conductive strip. 8.The wireless energy transfer unit according to claim 7, wherein saidspiral conductor coil is a square spiral.
 9. The wireless energytransfer unit according to claim 7, wherein said spiral conductor coilis a circular spiral.
 10. The wireless energy transfer unit according toclaim 7, wherein said conductor coil includes a plurality ofcrisscrossing portions along a length thereof such that a beginning andan end of the conductor coil are positioned adjacent to one another. 11.The wireless energy transfer unit according to claim 5, wherein saidconductor coil includes a plurality of crisscrossing portions along alength thereof such that a beginning and an end of the conductor coilare positioned adjacent to one another.
 12. A wireless energy transferunit having at least one resonant frequency, comprising: an energycoupling/extraction conductor; and a multi-layer wireless energytransfer cell magnetically coupled to said energy coupling/extractionconductor, said multi-layer wireless energy transfer cell comprising: atop layer and a bottom layer, said top layer and said bottom layer beingmade of a magneto-electric material that produces an electric field whenexposed to a magnetic field; a first conductor layer forming a firstelectrode positioned adjacent to said top layer; a second conductorlayer forming a second electrode positioned adjacent to said bottomlayer; and a central layer positioned between said first conductor layerand said second conductor layer, said central layer being made of apiezoelectric material which resonates in response to an electric fieldbeing applied thereto by said first conductor layer and said secondconductor layer.
 13. A wireless energy transfer unit having at least oneresonant frequency, comprising: an energy coupling/extraction conductor;and a multi-layer wireless energy transfer cell magnetically coupled tosaid energy coupling/extraction conductor, said multi-layer wirelessenergy transfer cell comprising: a first coil element including a firstinsulator layer and a first conductor coil provided on said firstinsulator layer, said first conductor coil including a plurality offirst crisscrossing portions along a length thereof such that a firstbeginning and a first end of said first conductor coil are positionedadjacent to one another; a second coil element including a secondinsulator layer and a second conductor coil provided on said secondinsulator layer, said second conductor coil including a plurality ofsecond crisscrossing portions along a length thereof such that a secondbeginning and a second end of said second conductor coil are positionedadjacent to one another; and an insulator element made of an insulatingmaterial provided between said first coil element and said second coilelement; wherein said first coil element and said second coil elementare electrically connected to one another.
 14. The wireless energytransfer unit according to claim 13, wherein said first coil element andsaid second coil element are electrically connected to one anotherthrough said insulator element.
 15. The wireless energy transfer unitaccording to claim 14, wherein said first beginning of said first coilelement is electrically connected to said second end of said second coilelement.
 16. The wireless energy transfer unit according to claim 13,wherein said multi-layer wireless energy transfer cell furthercomprises: a third coil element including a third insulator layer and athird conductor provided on said third insulator layer, said thirdconductor coil including a plurality of third crisscrossing portionsalong a length thereof such that a third beginning and a third end ofsaid third conductor coil are positioned adjacent to one another; and asecond insulator element made of an insulating material provided betweensaid second coil element and said third coil element; wherein saidsecond coil element and said third coil element are electricallyconnected to one another.
 17. The wireless energy transfer unitaccording to claim 16, wherein said first coil element and said secondcoil element are electrically connected to one another through saidinsulator element and said second coil element and said third coilelement are electrically connected to one another through said secondinsulator element.
 18. The wireless energy transfer unit according toclaim 17, wherein said first beginning of said first coil element iselectrically connected to said second end of said second coil element,and said second beginning of said second coil element is electricallyconnected to said third end of said third coil element.
 19. The wirelessenergy transfer unit according to claim 13, wherein said first coilelement, said second coil element and said insulator element aredisk-shaped.
 20. The wireless energy transfer unit according to claim16, wherein said first coil element, said second coil element, saidthird coil element, said insulator element, and said second insulatorelement are disk-shaped.
 21. The wireless energy transfer unit accordingto claim 13, wherein said first conductor coil and said second conductorcoil are each film coils.
 22. The wireless energy transfer unitaccording to claim 13, wherein said first conductor coil, said secondconductor coil and said third conductor coil are each film coils.
 23. Awireless energy transfer unit having at least one resonant frequency,comprising: an energy coupling/extraction conductor; and a multi-layercylindrical wireless energy transfer cell magnetically coupled to saidenergy coupling/extraction conductor, said multi-layer cylindricalwireless energy transfer cell comprising: an inner cylindricalinsulator; a first spiral conductor coil provided on a surface of saidinner cylindrical insulator; an insulator layer provided on top of saidfirst spiral conductor coil; and a second spiral conductor coil providedon a surface of said insulator layer, said second spiral conductor coilbeing electrically connected to said first spiral conductor coil. 24.The wireless energy transfer unit according to claim 23, wherein saidfirst spiral conductor coil is oriented in one of a positive angle and anegative angle with respect to a longitudinal axis of said innercylindrical insulator, and wherein said second spiral conductor coil isoriented in the other of said positive angle and said negative anglewith respect to said longitudinal axis of said inner cylindricalinsulator.
 25. The wireless energy transfer unit according to claim 24,wherein said first spiral conductor coil includes a plurality of firstenlarged portions along a length thereof, wherein said second spiralconductor coil includes a plurality of second enlarged portions along alength thereof, and wherein each of said second enlarged portionscorresponds to and overlaps a respective one of said first enlargedportions.
 26. The wireless enemy transfer unit according to claim 25,wherein each of said first enlarged portions and each of said secondenlarged portions is disk-shaped.
 27. The wireless energy transfer unitaccording to claim 23, wherein said multi-layer cylindrical wirelessenergy transfer cell further comprises a ferrite core provided insidesaid inner cylindrical insulator.